1. Field of the Invention
The present invention relates to a nanocomposite, and specifically relates to a nanocomposite comprising a nanostructure and a polymer adsorbed to the nanostructure. The present invention further relates to a dispersion comprising the nanocomposite.
2. Related Background Art
Carbon-based nanofillers represented by a carbon nanotube (CNT) are excellent in thermal conductive properties, electrical conductive properties, mechanical properties and the like. Accordingly, addition of such a nanofiller to a solvent, a resin, a metal and a ceramic has been actively examined to provide these materials with the aforementioned properties. Moreover, boron nitride-based nanofillers, represented by a boron nitride nanotube and a BCN nanotube obtained by replacing some carbon atoms in a carbon nanotube with a nitrogen atom and a boron atom, are also excellent not only in thermal conductive properties and the like, but also in electrical insulating properties unlike the carbon-based nanofillers. Hence, the boron nitride-based nanofillers attract attention as a function-providing material. However, these nanofillers are likely to aggregate by the van der Waals force, and dispersibility thereof is extremely low in a solvent and in a resin. This brings about a problem that the nanofillers can insufficiently exert the above properties.
In this aspect, various methods have been proposed to improve the dispersibility of carbon nanotubes in a solvent.
For example, International Publication No. WO2002/016267 (Literature 1) discloses a composition comprising a carbon nanotube coated at least in part with at least one polymer. The polymer is exemplified by hydrophilic polymers such as polyvinyl pyrrolidone, polystyrene sulfonate, and polyethylene glycol. Moreover, International Publication No. WO2002/076888 (Literature 2) discloses a powder in which a hydrophilic polymer is adsorbed on a carbon nanotube. The polymer is exemplified by gum arabic, carrageenan, pectin, and the like. Further, Valerie C. Moore, et al., Nano Lett., 2003, volume 3, pp. 1379-1382 (Literature 3) discloses a single-walled carbon nanotube dispersed in an aqueous medium using various surfactants. As an ionic surfactant, an anionic surfactant such as sodium dodecylbenzenesulfonate, a cationic surfactant such as cetyltrimethylammonium bromide, and the like are disclosed. By thus using the hydrophilic polymer or the ionic surfactant together with the carbon nanotube, the dispersibility of the carbon nanotube in water tends to be improved. However, even with use of such a hydrophilic polymer or ionic surfactant, it has been difficult to obtain a dispersion of a carbon nanotube having a high concentration and excellent dispersion stability.
Additionally, Petar Petrov, et al., Chem. Commun., 2003, pp. 2904-2905 (Literature 4) discloses a composite comprising a carbon nanotube and a polymer containing a pyrenyl group that can be physically adsorbed to the carbon nanotube. The polymer adsorbed to the carbon nanotube tends to improve dispersibility of the carbon nanotube in an organic solvent. Nevertheless, dispersibility of this composite in an aqueous solvent is insufficient.
Japanese Unexamined Patent Application Publication No. 2010-37537 (Literature 5) discloses a carbon nanocomposite in which a vinyl-based polymer having a pyrenyl group-containing side chain and a polyethylene glycol-side chain is adsorbed to a carbon nanostructure. It is disclosed that this carbon nanocomposite exerts excellent dispersibility not only in an organic solvent such as chloroform but also in water. However, the carbon nanocomposite does not have a sufficient dispersibility in hot water.
In addition, Xinlu Li, et al., Carbon, 2006, Volume 44, pp. 1334-1336 (Literature 6) discloses that it is effective to add a carbon-based nanofiller such as a carbon nanotube to a battery cathode material in order to improve electronic conductivity of the battery cathode material. Dispersibility of the carbon-based nanofiller in the cathode active material needs to be improved in order to exhibit excellent battery performance. However, the addition and mixing of the carbon-based nanofiller by a conventional dry method have a limitation in the improvement.
In this connection, Jiajun Chen, et al., Electrochemistry Communications, 2006, volume 8, pp. 855-858 (Literature 7) discloses a method for producing a composite where a carbon-based nanofiller is dispersed in an active material, comprising: dissolving a raw-material compound of the active material containing, for example, Li Co, Ni, Mn, Fe and P, in a dispersion comprising the carbon-based nanofiller and an aqueous solvent; and subjecting the mixture to a hydrothermal reaction at a temperature of 150 to 200° C., followed by a heat treatment (for example, 500° C. or higher) in an inert gas. However, even by use of this method, dispersibility of the carbon-based nanofiller in the active material is insufficient. Further improvement in the dispersibility of a carbon-based nanofiller in a high-temperature aqueous solvent during a hydrothermal reaction has been demanded.